The invention us directed to a low-inductance electrolytic capacitor having a pot accepting a winding and an insulating terminating disk into which a positive lead-through and a negative lead-through for the winding are introduced.
DE-U-298 20 720 discloses an electrolytic capacitor wherein a resin-bonde paper disk reinforced with a metal plate is employed instead of the known terminating disk composed of plastic in order to reduce the inductance.
Given rapid switching events, as known, the self-inductance of electrolytic capacitors effects a delay of their smoothing function for the voltages. Various efforts have already been made to reduce the self-inductance of electrolytic capacitors in order to keep this delay as low as possible (see, for example, DE 297 18 066 U1). Many of these efforts aim at reducing individual inductances that all contribute to the overall inductance of an electrolytic capacitor. Nonetheless, a low-inductance electrolytic capacitor has not yet been successfully created that is distinguished by such a low self-inductance that a delay of the smoothing function for voltages can be avoided given rapid switching events.
It is therefore an object of the present invention to specify a low-inductance electrolytic capacitor that is distinguished by an extremely low self-inductance, so that a delay of its smoothing function for voltages can be practically largely avoided.
This object is inventively achieved by an electrolytic capacitor having a pot accepting a winding and having an insulating disk into which a positive lead-through and a negative lead-through for the winding are introduced, the capacitor having an electrically conductive disk at least in the region between the pot edge and the negative lead-through and electrically separated from the positive lead-through, the conductive disk being electrically conductively connected to a flared flange on an edge of the pot and electrically contacting the negative lead-through at an end facing away from the winding.
The invention thus embarks upon a path that departs completely from the previous state of the art. Instead of having recourse to measures that aim at a reduction of the individual inductances, as has been hitherto standard, an additional current path for high-frequency currents is constructed given the new, low-induction electrolytic capacitor that is laid for the minus contact between the winding of the electrolytic capacitor via the pot floor to the negative lead-through. To this end, the electrically conductive disk is provided at least in the region between the pot edge, which, of course, is connected via the pot casing to the pot floor, and the negative lead-through, whereby this electrically conductive disk, of course, is arranged electrically separated from the positive lead-through. For example, a current path between the pot of the electrolytic capacitor and the negative lead-through is constructed without further ado with a standard screw-type terminal in an electrolytic capacitor.
The electrically conductive disk is preferably composed of metal and, for example, is secured and electrically contacted to the upper flared flange of the pot and the negative lead-through. A hole for the positive lead-through is provided in the disk, and additional holes that allow the electrolytic capacitor or, respectively, its terminating disk to be viewed can be potentially provided.
The disk applied in the new low-inductance electrolytic capacitor serves the sole purpose of opening up the additional current path for high-frequency currents for the negative contact between winding via the pot floor to the negative lead-through. The disk assumes no further functions such as, in particular, mechanical fastening tasks, etc. For this reason, the disk can be implemented in a simple way and, for example, can be composed of a metal lattice, a wire net or even of correspondingly conducted individual wires. The expression xe2x80x9cdiskxe2x80x9d is thus to be understood very broadly and is intended to cover any xe2x80x9cdisk-shapedxe2x80x9d arrangement that is in the position of producing the desired electrical connection.
In existing electrolytic capacitors with a solder star, the current is in fact conducted from the winding to the negative contact via the housing, i.e. the pot. In such an electrolytic capacitor, however, there is only this single electrical connection between the negative contact and the winding.
Differing therefrom, the new low-inductance electrolytic capacitor has both the usual, direct connection between upper side of the winding and negative contact or, respectively, negative lead-through as well as the additionally provided, xe2x80x9cindirectxe2x80x9d connection via the pot floor, pot and disk. Given the inventive low-inductance electrolytic capacitor, the current can thus xe2x80x9cdividexe2x80x9d, which leads to a corresponding reduction of the self-inductance of the electrolytic capacitor.
A critical advantage of the new low-inductance electrolytic capacitor is to be seen that the disk provided therein, which forms a critical feature of the invention, can also be installed without further ado in existing electrolytic capacitors. In other words, the application of the invention in existing electrolytic capacitors requires no difficult retrofitting for reducing the self-inductance.
The self-inductance can be reduced by about one-third through one-fourth by the planar electrical connection between the housing and the negative lead-through. Measurements undertaken by the inventor have shown that the inductances of electrolytic capacitors without the disk, having values of 17.7 nH, 14.8 nH or, respectively, 10.8 nH, can be reduced to values of 12.7 nH, 12.0 nH or, respectively, 7.65 nH given employment of a disk corresponding to the invention.
These values are obtained given utilization of a smooth or, respectively, planar disk that proceeds parallel to the surface of the terminating disk that is already present. In such an arrangement, the positive lead-through and the negative lead-through project beyond the disk since, in a preferred way as already set forth, the conductive disk is placed onto the flared flange of the pot and secured thereto.
In order to also reduce the current density in the upper region of the negative lead-through which projects beyond the disk, it is possible to design the disk so that the disk is initially contacted in the upper region of the negative lead-through. In other words, the disk contacts the negative lead-through at its end facing away from the winding. The self-inductance of the electrolytic capacitor can be reduced further in this way. However, greater demands are then to be made of the contactings of the electrolytic capacitor since the disk is arced xe2x80x9cupxe2x80x9d and proceeds practically in the plane of the end of the negative lead-through.
By employing a disk designed in this way, self-inductances in electrolytic capacitors of 17.7 nH or, respectively, 14.8 nH for capacitors without the disk can be reduced to values of 11.3 nH or, respectively, 10.0 nH for capacitors with the disk.
In order to additionally reduce the partial inductance of the positive lead-through, the disk can also be shaped so that the disks drops perpendicularly down to the height of the flared flange next to the positive lead-through, so that the disk has two different levels and the current in the disk can flow to the positive lead-through in a bifilar fashion. Given such a design of the disk, in other words, this proceeds up to the positive lead-through to a distance therefrom on the level of the upper end of the negative lead-through and, in the region of the positive lead-through, then drops onto the level of the flared flange of the pot. This is then what is referred to as a xc2xe disk.
It is likewise possible to make exactly half the area of the disk respectively available to the positive lead-through and the negative lead-through and to provide the vertical drop-off of the disk in the region between the negative lead-through and the positive lead-through. Although a inductance as low as that with the xc2xe disk cannot be achieved with such a design of the disk, what is referred to as a xc2xd disk, the contacting is less problematical since each lead-through, i.e. the positive lead-through and the negative lead-through, respectively has exactly half the area of the disk available to it for contacting.
As was initially set forth, the disk itself is preferably composed of metal, for example, aluminum. However, it is also possible to insulate the disk except for its contacting locations, i.e. to apply insulating material onto the disk composed in and of itself of metal, for example by coating, gluing, lacquering or enameling.
It is potentially possible to provide points of contact between the terminating disk and the disk, so that, for example, the disk presses against the terminating disk, as a result whereof the terminating disk of the electrolytic capacitor can be mechanically stabilized to prevent arching. Such a design of the disk for stabilizing the terminating disk also makes it possible to utilize thin terminating disks such as, for example, rubber-coated resin bonded paper disks.
Whereas it was assumed up to now that the disk is provided above the terminating disk at that side of the terminating disk facing away from the winding, this need not necessarily be so. On the contrary, the disk can also be arranged in the inside of the electrolytic capacitor, i.e. under the terminating disk. Given such a design, however, the self-inductance of the electrolytic capacitor is not lowered as much because the current must flow completely through the negative lead-through that then projects considerably from the terminating disk. In order to avoid too great an insulating outlay, the disk, given a disk lying under the terminating disk, can be secured to only that half of the terminating disk where the negative lead-through is placed. The advantage of such an embodiment is to be seen that the production sequencexe2x80x94except of the application of the disk on the underside of the terminating diskxe2x80x94and the outward appearance of the electrolytic capacitor remain unchanged. What is ultimately present here is merely a terminating disk modified by the disk in the region of the negative lead-through.
Given the inventive low-inductance electrolytic capacitor, it is advantageous that a connection of the pot to the winding is produced by additional impressions such as a middle bead or notches. The high-frequency currents that flow via the disk can thus proceed from the winding to the pot with a lower inductive impedance. In other words, it is possible in this way to further reduce the overall inductance of the inventive low-inductance electrolytic capacitor.
It has already been pointed out above that the disk can also be composed of a lattice or wire net. Finally, however, it is also possible to designationally coat the terminating disk with metal, so that this lamination assumes the function of the conductive disk. Aluminum is a suitable metal for this lamination since it can be applied without further ado by coating across the edge of the terminating disk into the interior of the electrolytic capacitor. A contacting then ensues via the pressure contact between the under edge of the terminating disk or, respectively, the lamination of the disk to the pot.